Here are the NFL rules when it comes to a blackout for NFL games including the playoffs:

Since 1973, the NFL has maintained a blackout policy that states that a home game cannot be televised locally if it is not sold out within 72 hours prior to its start time. Before 1973, all games were blacked out in their city of origin regardless of whether they were sold out. This rule, dating back to the NFL’s emerging years on television, resulted in home-city blackouts that even extended to championship games. For instance, the 1958 “Greates Game Ever Played” between the Baltimore Colts and New York Giants was not available on TV to New York fans despite the fact that tickets were out of reach to most. The Arizona Cardinals and Minnesota Vikings are trying to sell out their stadium for this year’s playoffs to avoid the harsh blackout rules. They are struggling to fill their respective stadiums.